Rock n Roller RR12 cart is the best/most capable of a great series of four wheelers. I have to move a cartload of equipment 100 yards over a gravel drive each year and the 4 inch fronts and 8 inch rear no flat tires handle it just fine. I used a handtruck with smaller tires the first year and it was a royal pain moving the cart over that gravel drive. The RR12 also has some stair climbing ability. The RocknRoller Series comes in several different sizes.
For use on smooth surfaces, the Magliner/Gemini four wheel carts are what UPS gives its drivers.
Another benefit is, they make an adjustable shelf unit for the Rock n Roller carts that has been very handy for setting up or even during load in. Comes on and off in a jif and can be used in the expanded mode of the cart or in the shrunken mode. I have 2 of the R n R carts and LOVE them.
NOW, with that said, they use non-standard sized innertubes so buy an extra or two for backup although in 10 plus years I've only had to replace 2 of them.